Modeling of Electron and Proton Transport in Chloroplast Membranes with Regard to Thioredoxin-Dependent Activation of the Calvin-Benson Cycle and ATP-Synthase

Using a mathematical model of light-induced processes of oxygenic photosynthesis, which takes into account the key stages of thioredoxin-dependent activation of the Calvin-Benson cycle and ATP-synthase, pHdependent regulation of electron and proton transport in chloroplasts has been studied. A comparison of computer simulations with experimental data on redox transients of photoreaction center P-700 showed that consideration of thioredoxin-dependent regulation was essential for adequate description of the multiphasic kinetics of P-700(+) induction. Within the framework of our model, the time courses of electron flow through PSI I and distribution of electron fluxes on the acceptor side of PSI in chloroplasts was described. It was demonstrated that the contributions of cyclic electron transport and electron flow to O-2 (the Mehler reaction) were significant during the initial phase of the induction period but diminished upon thioredoxin-dependent activation of the Calvin-Benson cycle.